Ready overseas once to include companion in play (7)
I believe the answer is:
drachma
'ready overseas once' is the definition.
(ancient currency or 'ready' of Greece)
'to include companion in play' is the wordplay.
'to include' means one lot of letters goes inside another.
'companion' becomes 'ch' (I've seen this in other clues).
'in play' becomes 'drama' ('drama' can be a synonym of 'play'. I am not sure about the 'in' bit.**).
'ch' put within 'drama' is 'DRACHMA'.
(Other definitions for drachma that I've seen before include "Old Greek coin" , "Former unit of money in Greece" , "money in the past" , "Formerly the basic unit of money in Greece" , "European currency replaced by the euro in 2002" .)